Ice detection is usually used in aviation during flight to indicate the presence of ice in air surrounding the aircraft.
The reliability and precision of this detection are very important since ice can deteriorate the properties of some parts of an aircraft, such as the aerodynamic properties of wing or engine intake parts, and increase the mass of the aircraft. This can then lead to loss of lift and controllability of the aircraft.
The detection assembly comprises an intrusive part immersed in the air flow surrounding the aircraft, and is typically placed at locations on the aircraft subject to particularly severe icing conditions, such as the aircraft nose or wings, to detect the first signs of ice appearance.
As shown in FIG. 1, a known detection assembly 100 comprises:                a mast 120; and        an elongated finger 110 installed on the mast 120 extending into the surrounding air.        
The finger 110 forms an oscillating sensitive element, typically excited by a magnetostrictive or piezoelectric device, with a eigen oscillation frequency sensitive to an ice deposit such that when ice accumulates on the finger 110, the mass of the finger 110 varies and the oscillation frequency changes until it being beyond a determined detection threshold. The ice detection signal is then triggered.
Optionally, this type of detection assembly 100 also comprises a heating system designed to temporarily de-ice the finger 110, in order to do a new ice detection. Thus, the detection assembly 100 is used in successive detection/de-icing cycles.
A Joule effect heating system is conventionally used.
However, this type of detection assembly 100 has a major disadvantage for ice detection around the icing conditions (static temperature of the surrounding air near 0° C.). Indeed, aircraft generates a modification of the aerodynamic field in its near environment (local pressure and speed) as it moves through the air. The detection assembly 100 is also subjected to this modification to the aerodynamic characteristics of the air flow. Thus, the equilibrium temperature of the detection assembly 100 will be less than the total temperature of the flow (temperature including the influence of speed) and will be higher than the static temperature of the environment in which the aircraft is moving, also called the OAT (Outside Air Temperature). The value of this equilibrium temperature above the OAT will increase as the aircraft speed increases.
Thus, when this OAT is equal to or slightly less than the icing temperature, the detection assembly according to prior art will not detect ice even if it is subjected to icing conditions.
A reduction in the aircraft speed bringing the equilibrium temperature of the detection assembly 100 close to the icing temperature will then cause ice appearance on the sensitive element that could have been detected earlier.
Those skilled in the art know that if a finger 110 is inclined at a suitably chosen angle and direction of inclination, the temperature on part of the surface of the finger 110 can be reduced. For example, FIG. 3 document U.S. Pat. No. 4,333,004 shows an inclined finger 110 of this type.
However, this system does not enable a large reduction in the equilibrium temperature, and does not enable any control over the value of this resulting temperature reduction.
Document U.S. Pat. No. 4,570,881 provides information about an ice detector 130 shown in FIG. 18 comprising a flexible membrane 132 to which a piezoelectric transducer 131 is fixed which, under electrical excitation, can vibrate the membrane 132 at a resonant frequency, the vibration frequency of the membrane then varying as a function of the stiffness modified by the accretion of ice on the membrane. This ice detector 130 also comprises a Peltier effect cooling and heating system 135, cooling and heating then being done within icing/de-icing cycles of the membrane.
Thus, the sensitive element of the ice detector 130 is characterised by a lower equilibrium temperature.
However, this ice detector 130 has a small detection area, and therefore ice detection may be not sufficiently reliable.
Furthermore, it only exposes a single detection face and does not extend in the three dimensions as the distance from the aircraft increases (as the said finger 110 does), which can reduce the quality of the result obtained.
Finally, the use of the Peltier effect implies a de-icing power of the same order of magnitude as the cooling power (of the order of a few watts). The power necessary for fast de-icing of the surface of the sensitive element is much higher (a few tens of watts). Thus, the Peltier system is not adapted to fast de-icing to facilitate a new detection.